1. Field of the Invention
The present invention relates to piezoelectric fans and air cooling apparatuses that vibrate blades by driving piezoelectric elements, thereby exhausting warm air from a heat source such as a heat sink.
2. Description of the Related Art
In recent years, because of a reduction in size and increasing component mounting density, portable electronic apparatuses have a problem with exhausting heat that is generated within the electronic apparatuses. In order to efficiently cool such electronic apparatuses by air cooling, air cooling apparatuses called piezoelectric fans have been proposed. In a piezoelectric fan using a piezoelectric element, as illustrated in FIG. 5, piezoelectric elements 22 are pasted on both surfaces of a planar metal plate 21 at one end, thereby forming a bimorph actuator portion 23 in the portion where the piezoelectric elements 22 have been pasted, one end of the actuator portion 23 is supported by a support member 24, and a plurality of comb-shaped blades 21a are formed on the other end of the metal plate 21. By inserting the blades 21a between fins 31, and driving the piezoelectric element 22, the blades 21a are excited, whereby warm air between the fins 31 is efficiently exhausted.
In a piezoelectric fan having this structure, since the blades 21a extend straight from the actuator portion, there is a problem in that the actuator portion 23 protrudes considerably outside of a heat sink 30, whereby the occupied volume becomes large. The blades 21a are displaced considerably as a result of the vibration of the piezoelectric element 22 being transmitted to the blades 21a. On the other hand, since the amplitude of the blades 21a is large, the piezoelectric element 22 also vibrates considerably due to the reaction. As a result, the load on the piezoelectric element increases and, hence, reliability may decrease due to, for example, generation of cracks in the piezoelectric element.
Japanese Unexamined Utility Model Registration Application Publication No. 02-127796 discloses a small fan in which one end of a piezoelectric element is fixed to a support member and a blade is attached to the other end of the piezoelectric element in a direction perpendicular to the extension direction of the piezoelectric element. In this case, lengths in the longitudinal and width directions can be reduced and, hence, there is an advantage in that the occupied space is reduced. However, this type of a fan has a structure in which a separately prepared blade is attached to the piezoelectric element using a connection member and, hence, stress is concentrated in the connection member portion. As a result, an excitation effect with long-term stability is not realized. In addition, since a structure is employed in which a single blade is attached to a single piezoelectric element, blades cannot be inserted between the plurality of fins of a heat sink and, hence, warm air between the fins cannot be efficiently exhausted.